Study finds man on the moon’s right eye impactor: a protoplanet

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The secret of the Imbrium Basin–the right eye of the man on the moon–is perhaps revealed in a new paper published by a professor from The Brown University. It says the feature was formed after a protoplanet–or a baby planet–hit it billions of years ago.

The paper’s estimates suggest that about three point eight billion years ago, an asteroid about the length of the state of New Jersey of the United States slammed into the surface of the moon. Previous estimates have suggested that the impactor was two times smaller in diameter and ten times less massive.

Pete Schultz, professor of earth, environmental and planetary sciences at the said university, said that the paper show the enormity of the object that slammed on moon. This, he added, is the first estimate of the Imbrium that is based largely on the moon’s geological features. Previous estimates were based solely on computer models, he said, and they claim that the slammer was only about fifty miles in diameter.

For the research, Schultz has used NASA’s laboratory impactor called The Vertical Gun Range which recreates galactic impacts on a small-scale environment. The facility employs a fourteen foot cannon that fires small projectiles at up to sixteen thousand miles per hour. The receivers they call impact planes, in addition to high-speed cameras, record the ballistic dynamics.

During the experiments, Schultz noticed that the impactors tend to start breaking apart when they first make contact with the surface. That point of initial contact is behind, or up-range, of the final crater where the bulk of the impactor digs into the surface. The agent that break-off the up-range of the final crater continue to travel at high speed, grooving and scouring the surface of the impact surface.

With the initial data, Schultz then worked with David Crawford of the Sandia National Laboratories who generated the computer models based on the same physics that would also happen at the surface of earth’s lunar neighbor.

Schultz, with an understanding of how the grooves were created, could use them to find the impact point of the Imbrium Basin. And because the fragments would have broken off from the either side of the impactor, he can use the groove trajectories to estimate the size of the impactor.

His calculations show that the diameter of the impactor was about one hundred and fifty miles across–or about two hundred and fifty kilometers–which is large enough for it to be classified as a protoplanet or a baby planet.

But that is a low-end estimate, said Schultz who claims that it could be as large as three hundred kilometers.

In addition, he and colleagues have used the similar methods to estimate the sizes of impactors of other moon features. For the Moscoviense and Orientale basins located at the natural satellite’s far side, they’ve found impactor sizes of one hundred, and one hundred and ten kilometers across, respectively. They were also larger than previous estimates.

These large crater makers, Schultz said, are records of ‘lost giants’ of the late heavy bombardment.

The moon, as it turns out, is where records of the past are available. Schultz believes that its scarred face can tell them quite a lot about what happened in our solar system three point eight billion years ago.

The research is titled ‘Origin and implications of non-radial Imbrium Sculpture on the Moon’; it was published via the Nature.